Method for drying laundry in a laundry treating appliance

ABSTRACT

A method of drying laundry in a laundry treating appliance having a treating chamber in which the laundry is received for drying comprises moving the treating chamber to redistribute the laundry, supplying air to the treating chamber to define a supply air flow, exhausting the supplied air from the treating chamber to define an exhaust air flow, heating the air supplied to the treating chamber by actuating a heater at full output to define a first heating phase and then cycling the heater ON/OFF to define a second heating phase.

BACKGROUND OF THE INVENTION

Laundry treating appliances, such as clothes dryers and combinationwasher/dryers may have a configuration based on a rotating drum thatdefines a treating chamber in which laundry items are placed for dryingaccording to a cycle of operation. The laundry treating appliance mayhave a controller operably connected with the various components of thelaundry treating appliance, including a heater, to execute the cycle ofoperation. During a cycle of operation, the laundry treating appliancemay supply air heated by the heater into a drum. Historically, theheater is turned on/off based on the temperature of the air exiting thetreating chamber to control the supply of heated air to the treatingchamber. While such a heater control is effective at ultimately dryingthe laundry, it does so by either oversupplying heat, especially whenshort dry times are desired, or having undesirably long dry times, whenlow heat is desired.

SUMMARY OF THE INVENTION

According to an embodiment of the invention, a method of drying laundryin a laundry treating appliance having a treating chamber in which thelaundry is received for drying comprises moving the treating chamber toredistribute the laundry, supply air to the treating chamber to define asupply air flow, exhausting the supplied air from the treating chamberto define an exhaust air flow and heating the air supplied to thetreating chamber by actuating a heater at full output until a maximumevaporation rate is met to define a first phase. The heater is thencycled ON/OFF to maintain the maximum evaporation rate to define asecond phase.

According to another embodiment of the invention, a method of dryinglaundry in a laundry treating appliance having a treating chamber inwhich the laundry is received for drying, comprises moving the treatingchamber to redistribute the laundry, supplying air to the treatingchamber to define a supply air flow, exhausting the supplied air fromthe treating chamber to define an exhaust air flow, receiving an inputindicative of at least one characteristic of the laundry in the treatingchamber and heating the air supplied to the treating chamber byactuating a heater at full output for a predetermined time, which isexperimentally determined to provide a maximum evaporation rate forlaundry having the at least one characteristic to define a first phase.The heater is then cycled ON/OFF to maintain the maximum evaporationrate to define a second phase.

According to another embodiment of the invention, a laundry treatingappliance for drying laundry according to a cycle of operation comprisesa rotatable drum at least partially defining a treating chamber, asupply air conduit fluidly coupled to the treating chamber, an exhaustair conduit fluidly coupled to the treating chamber, a fan fluidlycoupled to the supply air conduit, treating chamber, and exhaust airconduit to pass air from the supply air, into the treating chamber,where it is exhausted through the exhaust air conduit. A heaterthermally coupled to the supply air conduit heats the air in the supplyair conduit and a controller is operably coupled to the heater and thefan and programmed to supply air to the treating chamber and heat thesupplied air by actuating the heater at full output until a maximumevaporation rate is met to define a first phase. The heater is thencycled ON/OFF to maintain the maximum evaporation rate to define asecond phase.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a front perspective view of a clothes dryer, wherein theclothes dryer may be controlled based on a method according to oneembodiment of the invention.

FIG. 2 is a front schematic view of the clothes dryer of FIG. 1.

FIG. 3 is a schematic representation of a controller for controlling theoperation of one or more components of the clothes dryer of FIG. 1.

FIG. 4 is a flow-chart depicting a method according to one embodiment ofthe invention.

FIG. 5A is a graph illustrating the exhaust air flow temperature profileand moisture percentage profile during a cycle of operation.

FIG. 5B is a graph illustrating the heater ON/OFF time corresponding tothe exhaust air flow temperature profile of FIG. 6A.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates one embodiment of a laundry treating appliance in theform of a clothes dryer 10 according to an embodiment of the invention.While the laundry treating appliance is illustrated as a front-loadingdryer, the laundry treating appliance according to the invention may beanother appliance which performs a cycle of operation on laundry,non-limiting examples of which include a top-loading dryer, acombination washing machine and dryer; a tumbling or stationaryrefreshing/revitalizing machine; an extractor; a non-aqueous washingapparatus; and a revitalizing machine. The clothes dryer 10 describedherein shares many features of a traditional automatic clothes dryer,which will not be described in detail except as necessary for a completeunderstanding of the invention.

As illustrated in FIG. 1, the clothes dryer 10 may include a cabinet 12in which is provided a controller 14 that may receive input from a userthrough a user interface 16 for selecting a cycle of operation andcontrolling the operation of the clothes dryer 10 to implement theselected cycle of operation. The clothes dryer 10 will offer the user anumber of pre-programmed cycles of operation to choose from, and eachpre-programmed cycle of operation may have any number of adjustablecycle modifiers. Examples of such modifiers include, but are not limitedto chemistry dispensing, load size, a load color, and/or a load type.

The cabinet 12 may be defined by a chassis or frame supporting a frontwall 18, a rear wall 20, and a pair of side walls 22 supporting a topwall 24. A door 26 may be hingedly mounted to the front wall 18 and maybe selectively moveable between opened and closed positions to close anopening in the front wall 18, which provides access to the interior ofthe cabinet 12.

A rotatable drum 28 may be disposed within the interior of the cabinet12 between opposing front and rear bulkheads 30 and 32, whichcollectively define a treating chamber 34 having an open face that maybe selectively closed by the door 26. The drum 28 may include at leastone baffle or lifter 36. In most clothes dryers, there are multiplelifters 36. The lifters 36 may be located along the inner surface of thedrum 28 defining an interior circumference of the drum 28. The lifters36 may facilitate movement of laundry within the drum 28 as the drum 28rotates.

Referring to FIG. 2, an air flow system for the clothes dryer 10 isschematically illustrated and supplies air to the treating chamber 34and then exhausts air from the treating chamber 34. The air flow systemmay have an air supply portion that may be formed in part by a supplyair conduit 38, which has one end open to the ambient air and anotherend fluidly coupled to the treating chamber 34. Specifically, the supplyair conduit 38 may couple with the treating chamber 34 through an inletgrill (not shown) formed in the rear bulkhead 32. A fan 40 and a heater42 may lie within the supply air conduit 38 and may be operably coupledto and controlled by the controller 14. If the heater 42 is cycled on,the supplied air will be heated prior to entering the drum 28. The airsupply system may further include an air exhaust portion that may beformed in part by an exhaust air conduit 44. Operation of the fan 40draws air into the treating chamber 34 by the supply air conduit 38 andexhausts air from the treating chamber 34 through the exhaust airconduit 44. The exhaust air conduit 44 may be fluidly coupled with ahousehold exhaust duct (not shown) for exhausting the air from thetreating chamber 34 to the outside environment. However, other air flowsystems are possible as well as other arrangements of the fan 40 andheater 42. For example, the fan 40 may be located in the exhaust airconduit 44 instead of the supply air conduit 38.

The clothes dryer 10 may be provided with a temperature sensor 50 todetermine the temperature of the air in the exhaust air conduit 44. Oneexample of a temperature sensor 50 is a thermocouple. The temperaturesensor 50 may be operably coupled to the controller 14 such that thecontroller 14 receives output from the temperature sensor 50. Thetemperature sensor 50 may be mounted at any location in or near theexhaust air conduit 44 of the clothes dryer 10 such that the temperaturesensor 50 may be able to accurately sense the temperature of the exhaustair flow. For example, the temperature sensor 50 may be coupled thecabinet 12 in the area if the exhaust air conduit 44.

As is typical in a clothes dryer, the drum 28 may be rotated by asuitable drive mechanism, which is illustrated as a motor 46 and acoupled belt 48. The motor 46 may be operably coupled to the controller14 to control the rotation of the drum 28 to complete a cycle ofoperation. Other drive mechanisms, such as direct drive, may also beused.

The clothes dryer 10 may also have a dispensing system (not shown) fordispensing treating chemistries into the treating chamber 34. Thedispensing system may introduce treating chemistry into the drum 28 inany suitable manner, such as by spraying, dripping, or providing asteady flow of the treating chemistry. The treating chemistry may be ina form of gas, liquid, solid or any combination thereof and may have anychemical composition enabling refreshment, disinfection, whitening,brightening, increased softness, reduced odor, reduced wrinkling, stainrepellency or any other desired treatment of the laundry. Water is oneexample of a suitable treating chemistry. Other non-limiting examples ofsuitable treating chemistries are chromophore chemistry, softeningchemistry, and stain-repellency chemistry. In all cases, the treatingchemistries may be composed of a single chemical, a mixture ofchemicals, or a solution of water and one or more chemicals.

As illustrated in FIG. 3, the controller 14 may be provided with amemory 70 and a central processing unit (CPU) 72. The memory 70 may beused for storing the control software that may be executed by the CPU 72in completing a cycle of operation using the clothes dryer 10 and anyadditional software. The memory 70 may also be used to storeinformation, such as a database or table, and to store data receivedfrom the one or more components of the clothes dryer 10 that may becommunicably coupled with the controller 14.

The controller 14 may be operably coupled with one or more components ofthe clothes dryer 10 for communicating with and/or controlling theoperation of the component to complete a cycle of operation. Forexample, the controller 14 may be coupled with the fan 40 and the heater42 for controlling the temperature and flow rate of the air flow throughthe treatment chamber 34; the motor 46 for controlling the direction andspeed of rotation of the drum 28; the temperature sensor 50 forreceiving information about the temperature of the exhaust air flow; andthe user interface 16 for receiving user selected inputs andcommunicating information to the user. The controller 14 may alsoreceive input from various additional sensors 52, which are known in theart and not shown for simplicity. Non-limiting examples of additionalsensors 52 that may be communicably coupled with the controller 14include: a treating chamber temperature sensor, a supply air flowtemperature sensor, a moisture sensor, an air flow rate sensor, a weightsensor, and a motor torque sensor.

Generally, in normal operation of the clothes dryer 10, a user firstselects a cycle of operation via the user interface 16. The user mayalso select one or more cycle modifiers. In accordance with theuser-selected cycle and cycle modifiers, the controller 14 may controlthe operation of the rotatable drum 28, the fan 40 and the heater 42, toimplement the cycle of operation to dry the laundry. When instructed bythe controller, the motor 46 rotates the drum 28 via the belt 48. Thefan 40 draws air through the supply air conduit 38 and into the treatingchamber 34, as illustrated by the flow vectors. The air may be heated bythe heater 42. Air may be vented through the exhaust air conduit 44 toremove moisture from the treating chamber 34. During the cycle, treatingchemistry may be dispensed into the treating chamber 34. Also during thecycle, output generated by the temperature sensor 50 and any additionalsensors 52 may be utilized to generate digital data corresponding tosensed operational conditions inside the treating chamber 34. The outputmay be sent to the controller 14 for use in calculating operationalconditions inside the treating chamber 34, or the output may beindicative of the operational condition. Once the output is received,the controller 14 processes the output for storage in the memory 70. Thecontroller 14 may convert the output during processing such that it maybe properly stored in the memory 70 as digital data. The stored digitaldata may be processed in a buffer memory, and used, along withpre-selected coefficients, in algorithms to electronically calculatevarious operational conditions, such as a degree of wetness or moisturecontent of the laundry. The controller 14 may use both the cyclemodifiers specified by the user and the additional information obtainedby the sensors 50, 52 to carry out the desired cycle of operation.

The previously described clothes dryer 10 provides the structurenecessary for the implementation of the method of the invention. Severalembodiments of the method will now be described in terms of theoperation of the clothes dryer 10. The embodiments of the methodfunction to ensure proper drying of a load of laundry.

Referring to FIG. 4, a flow-chart depicting a method 80 for dryinglaundry according to one embodiment of the invention is shown, andincludes a more specific cycle of operation based on the normaloperation described above. The method 80 may be carried out by thecontroller 14 using information inputted by the user via the userinterface 16 and from the sensors 50, 52. The sequence of steps depictedis for illustrative purposes only and is not meant to limit the method80 in any way as it is understood that the steps may proceed in adifferent logical order, additional or intervening steps may beincluded, or described steps may be divided into multiple steps, withoutdetracting from the invention.

In general, the method 80 is based on the evaporation rate of themoisture from the laundry in the treating chamber. The method 80controls the ON/OFF of the heater to provide enough heat such that themoisture in the laundry load reaches a maximum evaporation rate and thenmaintains that maximum evaporation rate. The method 80 is accomplishedwithout supplying more heat than necessary to reach the maximumevaporation rate. In this way, the method 80 provides the fastestpossible drying time with the least amount of heat. The method 80provides an initial in-rush of heat to achieve the maximum evaporationrate and then cycles the heater ON/OFF to maintain the maximumevaporation rate in order to dry the laundry in the least amount of timeand with the least amount of energy consumption from the heater.

Looking at the details of the method 80, the method 80 comprises movingthe treating chamber 82 to redistribute the laundry, supplying air tothe treating chamber 84 to define a supply air flow, exhausting thesupplied air from the treating chamber 86 to define an exhaust air flow,heating the air supplied to the treating chamber by actuating a heaterat full output to define a first heating phase 88 and then cycling theheater ON/OFF to define a second heating phase 90. The first heatingphase 88 may include actuating a heater at full output until a maximumevaporation rate is met and the second heating phase 90 may includecycling the heater ON/OFF to maintain the maximum evaporation rate. Itwill be understood that the heater may have multiple output levels andthat actuating the heater at full output comprises actuating the heaterat one of the output levels.

Most heaters, be it electric or gas powered, operate at a full ON poweror a full OFF power and do not have variable power to generate variableheat outputs. A variable power heater would allow the heat output levelto be continuously changed in order to maintain an ideal maximumevaporation rate without cycling the heater ON/OFF. However, utilizing aheater which must be cycled ON/OFF at full power introduces componentlimitations such as heater cycle times and moisture generated by a gasheater flame ignition, which prevent a perfect maintaining of an idealmaximum evaporation rate. Therefore, it will be understood thatmaintaining the maximum evaporation rate as used in this descriptionwill be subject to these limitations and may not be a perfectmaintaining of the maximum evaporation rate, but refers to a maintainingof the maximum evaporation within the practical limitations of theparticular laundry treating appliance.

The method 80 may also include receiving an input indicative of at leastone characteristic of the laundry in the treating chamber wherein thefirst heating phase 88 includes actuating a heater at full output for apredetermined time, which is experimentally determined to provide amaximum evaporation rate for laundry having the at least onecharacteristic. The input may be supplied by a user or sensors and theat least one characteristic may include one or both of the size or typeof the load. The size may refer to the load size and be quantified byuser settings such as small, medium or large, or may be determined usingsensors such as a weight sensor. The load type may include specificfabric types such as cottons, linen, denim etc. or may include generalfabric types such as delicate, permanent press, etc.

Ideally, the method 80 would be able to accomplish the balance betweenmaintaining the maximum evaporation rate and minimizing the suppliedheat. With contemporary controllers, it would be possible to get closeto the ideal if a suitable controller, heater, and humidity sensor wereused. Such systems are less desirable because of their relative expense.Another approach, is to experimentally determine, for a given laundryload, the amount of heat needed to bring the load to the maximumevaporation rate and maintain it at the maximum evaporation rate untilthe desired amount of dryness is reached. Whether a sensor basedsolution is used or an experimental based system is used, neither systemwould perfectly maintain the maximum evaporation rate. Instead, eachapproach would, based on the controller and approach, maintain theevaporation rate as close as practical to the maximum evaporation ratefor that given controller and approach.

FIG. 5A shows a graph illustrating the outlet air temperature profile150 and moisture percentage profile 160 during a cycle of operation andFIG. 5B shows a graph illustrating the heater ON/OFF time during a cycleof operation, according to an embodiment of the invention. The firstheating phase corresponds to the initial ON time 120 of the heater.During the initial ON time 120, the heater is actuated ON at full outputuntil a maximum evaporation rate is met. The initial ON time 120 acts toheat the supply air, the laundry within the treating chamber and thelaundry treating appliance in order to meet the maximum evaporation rateand the time duration will be a function of the mass of the machine,mass of the load and the laundry type and will vary from appliance toappliance. It is for this reason that the initial ON time 120 will beexperimentally determined for each combination of appliance and loadtype.

During the initial ON time 120, the heater actuated at full output heatsthe supply air, the laundry within the treating chamber and the laundrytreating appliance until the moisture percentage in the laundry beginsto decrease at a constant rate due to the maximum evaporation rate beingmet. The point at which the maximum evaporation rate is met may bedefined as the maximum evaporation threshold value 148 such that meetingthe maximum evaporation rate includes satisfying the maximum evaporationthreshold value 148. The maximum evaporation threshold value 148 mayalso be defined as a point at which the initial profile curve 146 of theexhaust air flow temperature levels off or begins to level off, a pointon the initial profile curve 146 when a time rate of change of theexhaust air flow temperature drops below a predetermined rate or a pointwhen the initial profile curve 146 reaches a predetermined temperature.The maximum evaporation threshold value 148 indicates that the heatenergy supplied by the heater is being used to evaporate the moisturewithin the laundry load and that the maximum evaporation rate has beenmet.

The initial ON time 120 of the heater may be a predetermined time whichis experimentally determined to provide the maximum evaporation rate fora given laundry load and the full output of the heater. That is, uponpassing the predetermined time, the maximum evaporation threshold value148 is satisfied. The predetermined time may also be experimentallydetermined to provide the maximum evaporation rate for a given laundryload having at least one characteristic received by the laundry treatingappliance through an input indicative of the at least onecharacteristic. In this way, laundry loads having differentcharacteristics may have a different predetermined time for the initialON time 120 in order to satisfy the maximum evaporation threshold value148.

Once the maximum evaporation rate has been met during the initial ONtime 120, the heater is cycled OFF for a predetermined OFF time 130,starting the second heating phase. The predetermined OFF time 130 thatthe heater is cycled OFF may be experimentally determined to maintainthe maximum evaporation rate for a given laundry load. The predeterminedOFF time 130 acts to reduce energy of the appliance by turning OFF theheater while maintain the maximum evaporation rate and the time durationwill be a function of the mass of the machine, mass of the load and thelaundry type and will vary from appliance to appliance. It is for thisreason that the predetermined OFF time 130 will be experimentallydetermined for each combination of appliance and load type.

After the passing of a predetermined OFF time 130 from the heater beingcycled OFF, the heater is then cycled ON until a predetermined triptemperature 170 of the exhaust air flow has been met. The predeterminedtrip temperature 170 acts to allow the heater to supply enough heat tomaintain the maximum evaporation rate and the predetermined triptemperature 170 will be a function of the mass of the machine, mass ofthe load and the laundry type and will vary from appliance to appliance.It is for this reason that the predetermined OFF time 130 will beexperimentally determined for each combination of appliance and loadtype.

Cycling the heater OFF for a predetermined OFF time 130 and ON until apredetermined trip temperature 170 is met avoids issues related toambient conditions. For example, in a case where the heater is cycledOFF until a predetermined low temperature of the exhaust air flow isreached and the ambient temperature is above the predetermined lowtemperature, the heater would never cycle ON. In another example, in thecase where the heater is cycled ON for a predetermined time, the ambienttemperature may be low enough that the exhaust air flow does not reach adesired temperature and the maximum evaporation rate is not met. Incontrast, cycling the heater OFF for a predetermined OFF time 130 and ONuntil a predetermined trip temperature 170 is met avoids these issues.

During the second heating phase, the cycling of the heater ON/OFF iscontinued until the moisture percentage in the laundry load falls belowa predetermined moisture percentage level, indicating a dry laundryload. As the moisture percentage continues to decrease, less heat energyis needed to maintain the maximum evaporation rate which corresponds tothe exhaust air flow temperature reaching the predetermined triptemperature 170 in less time from the end of the previous OFF cycle. Thepredetermined moisture percentage level may be determined by the timethe heater is cycled ON falling below a predetermined time threshold,defining a final cycle ON time 144. As illustrated, the time of aninitial cycle ON time 142 of the heater in the second heating phase isless than the time of the final cycle ON time 144. Once the final cycleON time 144 falls below the predetermined time threshold, the secondheating phase may end and the heater may be cycled OFF. Thepredetermined time threshold may be experimentally determined to achievea moisture percentage for a given laundry load below the predeterminedmoisture percentage level.

The embodiments according the invention provide for a plurality ofbenefits including that the providing a method of drying laundry using afirst heating phase to meet a maximum evaporation rate and a secondheating phase the maintain the maximum evaporation rate allows thelaundry treating appliance to dry the laundry load with a minimum amountof energy and a minimum amount of sensors. By using an initialpredetermined ON time for the heater, the laundry and appliance are ableto be quickly brought up to a temperature that achieves the maximumevaporation rate of moisture in the laundry. Then by cycling the heaterON/OFF with predetermined times OFF and predetermined trip temperaturesON, the maximum evaporation rate may be maintain without wasting energyand while avoiding issues related to ambient conditions. Furthermore,the method of drying laundry is achieved using only an exhaust airtemperature sensor as an input, providing a laundry treating appliancecapable of carrying out the method with less manufacturing cost.

While the invention has been specifically described in connection withcertain specific embodiments thereof, it is to be understood that thisis by way of illustration and not of limitation, and the scope of theappended claims should be construed as broadly as the prior art willpermit. It should also be noted that all elements of all of the claimsmay be combined with each other in any possible combination, even if thecombinations have not been expressly claimed.

What is claimed is:
 1. A method of drying laundry in a laundry treatingappliance having a treating chamber in which the laundry is received fordrying, the method comprising: moving the treating chamber toredistribute the laundry; supplying air to the treating chamber todefine a supply air flow; exhausting the supplied air from the treatingchamber to define an exhaust air flow; receiving an input indicative ofat least one characteristic of the laundry in the treating chamber;determining a temperature of the exhaust air flow; and heating the airsupplied to the treating chamber by actuating a heater at full outputfor a predetermined time, which is experimentally determined to providea maximum evaporation rate for laundry having the at least onecharacteristic to define a first phase, and then cycling the heaterON/OFF to maintain the maximum evaporation rate to define a second phasewherein the heater is cycled ON until a predetermined trip temperatureof the exhaust air flow is met and cycled OFF for a predetermined timebased on at least one of: mass of the laundry treating appliance, massof a load, or laundry type.
 2. The method of claim 1 wherein the atleast one characteristic comprises at least one of size or type.
 3. Themethod of claim 2 wherein the at least one characteristic is comprisedboth of size and type.
 4. The method of claim 1 wherein the cycling theheater OFF during the second phase comprises cycling the heater OFF whena temperature of the exhaust air flow reaches a predeterminedtemperature set according to the at least one characteristic.
 5. Themethod of claim 4 wherein the cycling the heater ON during the secondphase comprises cycling the heater ON after the passing of apredetermined time, set according to the at least one characteristic,from the cycling the heater OFF.
 6. The method of claim 1 furthercomprising cycling the heater OFF between the first and second phases.7. The method of claim 6 wherein the heater is cycled OFF between thefirst and second phases for a predetermined time, which is set accordingto the at least one characteristic.
 8. A method of drying laundry in alaundry treating appliance having a treating chamber in which thelaundry is received for drying, the method comprising: moving thetreating chamber to redistribute the laundry; supplying air to thetreating chamber to define a supply air flow; exhausting the suppliedair from the treating chamber to define an exhaust air flow; and heatingthe air supplied to the treating chamber by actuating a heater at fulloutput until a maximum evaporation rate is met to define a first phasewherein the maximum evaporation rate is met when a maximum evaporatedthreshold value related to a temperature or rate of change of theexhaust air flow is satisfied and then cycling the heater ON/OFF tomaintain the maximum evaporation rate to define a second phase whereinthe cycling the heater ON/OFF comprises cycling the heater OFF when thetemperature of the exhaust air flow reaches a predetermined temperatureand wherein the heater is cycled OFF between the first and second phasesfor a predetermined time based on at least one of: mass of the laundrytreating appliance, mass of the laundry, or laundry type.
 9. The methodof claim 8 wherein the maximum evaporation threshold value is satisfiedwhen a temperature of the exhaust air flow levels off.
 10. The method ofclaim 9 wherein the temperature of the exhaust air flow levels off whena time rate of change of the exhaust air flow drops below apredetermined rate.
 11. The method of claim 8 wherein the maximumevaporation threshold value is satisfied upon passing of a predeterminedtime experimentally determined to provide the maximum evaporation ratefor a given load of the laundry and the full output of the heater. 12.The method of claim 8 wherein the cycling the heater ON/OFF comprisescycling the heater ON after the passing of a predetermined time from theheater being cycled OFF.
 13. The method of claim 8 wherein the actuatinga heater at full output comprises actuating a heater having multipleoutput levels at one of the output levels.
 14. The method of claim 8wherein the maximum evaporation threshold value is satisfied when a timerate of change of the exhaust air flow drops below a predetermined rate.15. The method of claim 8 wherein the maximum evaporated threshold valueincludes one of: a point at which a profile curve of a temperature ofthe exhaust air flow levels off or begins to level off, a point on theprofile curve when a time rate of change of the temperature of theexhaust air flow drops below a predetermined rate or a point when theprofile curve reaches a predetermined temperature.